- Polylithiumorganic compounds. Part 28. The reaction of allene and alkyl substituted allenes with lithium metal
-
The reaction of allene (3a) and alkyl substituted allenes 1,2-hexadiene (3b), cyclopropylallene (3c), and vinylidene cyclopropane (3d) with lithium metal was investigated in order to access 2,3-dilithioalkenes 4a-d. These dilithioalkenes 4a-d are very reactive in polar solvents like THF and act as strong bases, either metalation of the starting allene 3a-d, the solvent, or sufficiently acidic intermediates like 8 a-d is observed. The metalation products 5-7 show follow-up reactions like 1,3-H shift to the corresponding 1-lithio-1-alkynes 8 and subsequent metalation to the dilithioalkynes 9. Additionally, lithium hydride elimination and ring-chain rearrangement (for 5c) are observed. 1,2-Hexadiene (3b) can be brought to reaction with lithium metal in the apolar solvent pentane, here the follow-up reactions are much slower due to the insolubility of 4b. In all cases the elucidation of the reaction pathways is hampered by the formation of complex mixtures of, amongst others, regio- and stereoisomeric products upon quenching with simple electrophiles.
- Maercker, Adalbert,Tatai, Andrea,Grebe, Burkhard,Girreser, Ulrich
-
-
- Charge-reversal Mass Spectra of Enolate Ions of Some Open-chain and Cyclic Ketones for Structure Identification
-
The charge-reversal (CR) mass spectra of the enolate ions of heptanal and ten isomeric heptanones, of cyclohexanone, of cycloheptanone, of isomeric methylcyclohexanones, of isomeric ethylcyclohexanones and of the isomeric monoterpene ketones camphor, fenchone, pulegone and thujone were obtained by deprotonating using OH(-) under chemical ionization conditions followed by collision of the (-) ions with helium in the second field-free region of a VG ZAB 2F mass spectrometer.The CR mass spectra were evaluated by similarity index (SI) values.Characteristic of the CR mass spectra of the open-chain enolates are fragment ions formed by α- cleavage.However, the CR mass spectra are dominated by peaks of small hydrocarbon ions, particularly in the case of cyclic and bicyclic enolates.The CR mass spectra of enolates of linear heptanones differing in the position of the carbonyl group can be easily correlated with the structure of the parent ketone.The CR mass spectra of enolates of isomeric heptan-2-ones differing only in the degree of branching of the alkyl group are similar, but can be distinguished by the SI values.The CR mass spectra of the enolates of the isomeric cyclic and bicyclic ketones studied are more or less identical and cannot be used for structural assignment.
- Suerig, Thomas,Gruetzmacher, Hans-Friedrich
-
p. 446 - 452
(2007/10/02)
-
- Mechanistics Studies on the Cobalt(II) Schiff Base Catalyzed Oxidation of Olefins by O2
-
The cobalt complex cobalt(II), CoSMDPT, has been shown to catalystically oxidize olefins in the presence of dioxygen or hydrogen peroxide.When terminal olefins are oxidized, the methyl ketone and corresponding secondary alcohol are produced selectively.Internal as well as terminal olefins are oxidized.The most common pathway for the oxidation of olefins catalyzed by first-row transition metals - autoxidation - has been ruled out in this system.A Wacker-type mechanism, oxidation by peracids, and mechanisms involving the formation of peroxymetallocycles have also been ruled out.A new mechanism for O2 oxidations is proposed which involves oxidation of the primary alcohol solvent by CoSMDPT to produce the corresponding aldehyde and hydrogen peroxide.Reaction of hydrogen peroxide with CoSMDPT occurs to form a cobalt hydroperoxide, which can be viewed as a stabilized hydroperoxy radical which has spin paired with the dz2 electron of CoSMDPT.The cobalt hydroperoxide then adds to the olefin double bond, leading to formation of an alkyl hydroperoxide.Haber-Weiss decomposition of this alkyl hydroperoxide by CoSMDPT produces the observed ketone and alcohol products.Deactivation of the catalysts is due to oxidation of the ligand system of the cobalt complex as well as formation op a μ-peroxo-dicobalt complex.
- Hamilton, Dorothy E.,Drago, Russell S.,Zombeck, Alan
-
p. 374 - 379
(2007/10/02)
-
- THE REACTION OF β-STANNYL CARBONYL COMPOUNDS WITH LEWIS ACIDS
-
β-Stannyl carbonyl compounds, when treated with Lewis acids, afforded cyclopropane derivatives or ketones, and the reaction was applied to the synthesis of β,γ-enones from α,β-enones.
- Sato, Tadashi,Watanabe, Masami,Murayama, Eigoro
-
p. 1621 - 1624
(2007/10/02)
-